Timescales of magma transfer in intraplate volcanic systems from diffusion modelling of lithium isotopes in zircon and olivine

以岩浆转移和上升速度的时间尺度衡量的地壳中岩浆的动态行为是一个关键的未知数，它限制了对火山爆发和有关灾害进行更可靠的监测。由于动态岩浆系统中存在各种化学不平衡，应用固体或熔体中的扩散定律可以指导对许多岩浆过程速率的定量一级约束的提取。在这一建议中，锂在锆石和橄榄石中的快速扩散被认为是一个强有力的组合，用于表征板内火山岩场从源到喷口的岩浆管道系统。然而，这些定量方法的可靠性，需要彻底了解锂在这两种矿物中的分布和动力学行为。正在进行的幔源锆石锂同位素研究的初步结果提供了强有力的支持的假设，锂在锆石扩散的建模具有特殊的潜力，以限制岩浆从存储到喷发的持续时间。结果可以通过模拟锂在橄榄石中的扩散来进一步交叉检查，这种扩散已经成功地用于研究短期岩浆过程。锂丰度和同位素比值锆石从地壳捕虏体和橄榄石从玄武岩寄主岩石将进行调查，以确定热激活扩散的时间尺度，可以转化为岩浆转移和上升速率的捕虏体夹带深度的合理假设。从锆石的拉曼光谱推断的退火持续时间和岩浆中捕虏体的平均沉降速率允许进一步验证从锆石和橄榄石中的Li扩散提取的速率。建议研究的地壳捕虏体和寄主玄武岩样品来自三个具有不同地壳特征的板内火山岩区，它们是中央地块（法国），库拉（土耳其）和汉诺巴（中国）。预计该研究将为深入了解天然系统中锆石和橄榄石中的锂扩散提供帮助。锂扩散测时法结合锆石拉曼光谱对退火时间的限制，有望为推断地壳水平岩浆迁移时间尺度和岩浆上升速率提供有意义的数据，从而进一步发展锂同位素作为高温岩浆过程的新兴地质速度计和岩石学示踪剂的应用。

The dynamic behaviour of magma in the crust as measured by timescales of magma transfer and ascent rates is a key unknown limiting development of more reliable monitoring of volcanic eruptions and related hazards. As a result of various chemical disequilibria in dynamic magmatic systems, applying the laws of diffusion in solids or melts can guide the extraction of quantitative, first-order constraints on the rates of many magmatic processes. In this proposal, the fast diffusion of Li in zircon and olivine is proposed as a powerful combination for characterizing the magmatic plumbing systems from source to vent in intraplate volcanic fields. The reliability of these quantitative methods, however, requires a thorough understanding of the distribution and kinetic behaviour of Li in both minerals. Preliminary results of an ongoing study of Li isotopes in mantle-derived zircon lend strong support to the assumption that modelling of Li-in-zircon diffusion has an exceptional potential to constrain the duration of magma from storage to eruption. Results can be further cross-checked by modelling Li-in-olivine diffusion which has been already successfully utilized to investigate short-term magmatic processes. Li abundances and isotopic ratios in zircon from crustal xenoliths and olivine from their basaltic host rocks will be investigated to determine thermally activated diffusion timescales which can be translated into magma transfer and ascent rates for reasonable assumptions regarding the depth of xenolith entrainment. Annealing durations inferred from Raman spectroscopy of zircon and the average settling rate of xenoliths in magma allow further validation of rates extracted from Li diffusion in zircon and olivine. Samples of crustal xenoliths and host basalts for the proposed study stem from three intraplate volcanic fields with distinct crustal characteristics, which are the Massif Central (France), Kula (Turkey), and Hannuoba (China). It is expected that the study provides an in-depth understanding of Li-diffusion in zircon and olivine in natural systems. Li-diffusion chronometry combined with Raman spectroscopy of zircon to constrain annealing durations is expected to provide meaningful data for inferring timescales of magma transfer and magma ascent rates at crustal levels, thereupon further developing the application of Li-isotopes as an emerging geospeedometer and petrological tracer for high temperature igneous processes.